As a fuser used in an image forming apparatus such as a copying machine or a printer, there is a fuser in which the heat capacity of a heat generating part is reduced, the energy is saved, and a quick temperature rise is achieved. The heat generating part having the small heat capacity is difficult to keep the surface temperature of the heat generating part uniformly in a direction perpendicular to the conveyance direction of a sheet.
In the heat generating part having the small heat capacity, heat transfer from the heat generating part to the sheet does not occur in a sheet non-passing region during fixation, and there is a fear that an abnormal increased temperature occurs. Because of the increased temperature of the sheet non-passing region, there is a fear that the image forming operation of the image forming apparatus must be placed in a stand-by state.